MHS Chemistry
Behavior of Gases
Pressure & Volume

This purpose of this lab is to examine the quantitative relationship between gas pressure and gas volume.

Procedure

1. Set the plunger at the highest mark of a dry syringe.
2. Set up the lab apparatus as shown by your instructor.
3. Carefully center a textbook on top of the plunger block.  Read as precisely as possible the volume of gas trapped in the plunger.  Record this volume.  Remove the textbook.  You may notice the plunger doesn't return to the original volume when the books are removed.  This is due to friction between the plunger and the syringe.  Do not attempt to correct it.
4. Now place 2 textbooks on the plunger block and read & record the volume.  Next place three books on the plunger block and read & record the volume.  Continue until you have placed 6 textbooks on top of the plunger.  You may find a problem with balance.  Work carefully to balance the books. Supporting the apparatus with your hand may cause error in your data.
5. Repeat the entire experiment until you have obtained five good trials.
Analysis
1. For each pressure, calculate the average volume and the average deviation (“AD”).  Average Deviation is the average absolute difference between each measurement and the average.  (Say it slowly!)
2. Graph your data with Pressure (measured in books) on the y-axis and Average Volume (measured in mL) on the x-axis.  Remember to use the whole page.  For each pressure, also plot the maximum volume (Vavg + AD) and the minimum volume (Vavg – AD).  Draw the best smooth curve through these ranges.  Can you determine a formula to get pressure from volume?  In math class it would be of the form y = f(x), or P = f(V).  See if your calculator can do this for you (the equation for this graph is for bonus points).
3. For each pressure, calculate 1/(Vavg + AD) and 1/(Vavg – AD).  Plot these numbers on another graph, making sure to use a new scale on the x-axis.
4. Draw the best straight line through this second set of ranges.  Continue this line until it intersects the y-axis.  You may need to attach an extra piece of graph paper for this to be possible.
5. Using skills from algebra, find the slope of this line, and the y intercept (include units on both of these).  Write out the equation for this line (it will be of the form y = mx+b).  The equation for this line is NOT bonus: it is required.  Answer this question on the graph sheet.
6. What does the value of the y intercept represent (physically, not mathematically)?
7. What will be the pressure when the volume 10.0 mL?
8. What will be the pressure when the volume is 100.0 mL?
9. What would be the volume under a pressure of 15 books?
Data & Results Table
 P (books) V (mL) AD (mL) __1__ __1__ __1__ trial 1 trial 2 trial 3 trial 4 trial 5 (avg) (±) Vavg Vavg+AD Vavg-AD 0 _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ 1 _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ 2 _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ 3 _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ 4 _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ 5 _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ 6 _______ _______ _______ _______ _______ _______ _______ _______ _______ _______ 7 _______ _______ _______ _______ _______ _______ _______ _______ _______ _______

5.    slope (m) = _______________                y-intercept (b) = _______________

equation: _________________________________________________________

6.

7.

8.

9.

Note: Each person should hand in their own copy of this lab.  Staple your graphs to these pages before you hand them in.